Both mice and men can find vasectomies a pain. That's what grimaces on the faces of the rodents suggest, thanks to our improved understanding of how rodents express pain.

Scientists want to better know when mice feel pain. There are animal welfare issues of not causing undue suffering, and scientific reasons as well — researchers would like to know when a therapy causes or relieves pain.

Recently, scientists developed a way to measure pain called the Mouse Grimace Scale. Just as people grimace after getting hurt, so too do rodents have pained expressions — their eyes squint, their ears pull back, and their noses and cheeks bulge.

To see how well the scale works, investigators looked at mice who received vasectomies. Scientists apparently carry out the little snips on mice all the time, especially on genetically modified mice, presumably to control how they breed.

As expected, mice apparently grimaced more after vasectomies. They also grimaced less when given painkillers. Science!!!